ABSTRACT
Various dialkyl azodicarboxylates were investigated for the dehydrogenation of 1,2,3,4-tetrahydroquinolines to quinolines. The dehydrogenation rates varied according to the electronic and steric nature of the used dialkyl azodicarboxylates. Among solvents screened with diethyl azodicarboxylate, chloroform exhibited superior results to others. A variety of 1,2,3,4-tetrahydroquinolines underwent the present dehydrogenation to produce the corresponding quinolines. Diethyl hydrazodicarboxylate, which is a reduced species of diethyl azodicarboxylate, was easily separated for recycle.
GRAPHICAL ABSTRACT
Notes
1Instead of CHCl3, the use of other solvents such as CH3CN and dichloroethane (DCE) at 70 °C also gave high product yields. For example, the yields of 2i were 97% in CH3CN and 96% in DCE at 70 °C.